1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, a production method thereof, and an information processing apparatus having the photoelectric conversion apparatus and, more particularly, to a photoelectric conversion apparatus used in an image input unit of digital X-ray detectors and X-ray image pickup apparatus for medical use, office equipment such as digital copiers, electronic blackboards, facsimile machines, and so on, and information processing apparatus, a production method of the photoelectric conversion apparatus, and an information processing apparatus having the photoelectric conversion apparatus.
2. Related Background Art
The mainstream of the existing X-ray image pickup apparatus used for medical diagnosis is of the so-called film method in which a human body is exposed to X-rays, X-rays transmitted by the human body are made incident to a fluorescent material for converting X-rays to visible light, and a film is exposed to fluorescence emitted from the fluorescent material.
There are, however, strong desires for increase of diagnosis efficiency and for medical equipment with higher accuracy in hospitals, not only in Japan about to go into aging society, but also in the world. Under such circumstances, the conventional X-ray image pickup apparatus of the film method requires long time because of the development step of film in the way before a doctor obtains an X-ray image of a patient, and there are some cases necessitating rephotography, where the patient moved during the X-ray photography or where exposure was not correct. These are the cause of impeding increase of efficiency of medical treatment in the hospitals and would be great hindrance to movement toward new medical society in the future.
In recent years, the demand for xe2x80x9cdigitization of X-ray image informationxe2x80x9d is increasing in the medical field. Accomplishment of the digitization will permit the doctor to capture the X-ray image information of the patient at the optimal angle in real time and also permit the X-ray image information obtained to be recorded and managed by use of a medium such as a magnetooptical disk or the like. It will also becomes possible to send the X-ray image information of patient to any hospital in the world within short time by making use of facsimile or other communication method or the like.
In order to meet the demand for the xe2x80x9cdigitization of X-ray image information,xe2x80x9d the X-ray image pickup apparatus using CCD solid state image sensing elements or amorphous silicon photoelectric conversion elements in place of the film has been proposed in recent years.
FIG. 1 is an equivalent circuit diagram to show an example of an equivalent circuit of a two-dimensional photoelectric conversion apparatus. FIG. 1 shows the two-dimensional photoelectric conversion apparatus of 3xc3x973 for simplicity of description, but the photoelectric conversion apparatus in practice is composed of much more bits, though depending upon the purpose of the apparatus.
Light incident to photoelectric conversion elements S1-1 to S3-3 is subjected to photoelectric conversion in a photoelectric conversion layer and the light information is stored in the form of a charge of a photoelectrically converted signal in a capacitor between electrodes of each photoelectric conversion element. These photoelectric conversion signals are converted to parallel voltage outputs through transfer switches T1-1 to T3-3 and matrix signal wires M1 to M3. Further, they are converted to serial signals by a reading switch circuit unit to be extracted to the outside.
In the structural example of the photoelectric conversion apparatus of FIG. 1, the photoelectric conversion elements having the total pixel number of 9 bits are divided into three rows, each row including three bits. The above-stated operations are carried out successively in every unit of these rows.
FIG. 2 is a timing chart to show the operation of the conventional photoelectric conversion apparatus illustrated in FIG. 1.
Information of light incident to the photoelectric conversion elements S1-1 to S1-3 in the first row is subjected to photoelectric conversion into signal charges and the signal charges are stored as respective interelectrode capacitances in the photoelectric conversion elements S1-1 to S1-3. After a lapse of a fixed storage time, a shift register SR1 gives the gate driving wire G1 a first voltage pulse for transfer during a period of time T1 to switch the transferring switching elements T1-1 to T1-3 on. This causes the signal charges stored in the respective electrode capacitors (S1-1 to S1-3) in the photoelectric conversion elements to be transferred through the matrix signal wires M1 to M3 to load capacitors C1 to C3, whereupon potentials V1 to V3 of the respective load capacitors are increased each by amount equal to the charge of each signal (transfer operation).
Subsequent to it, another shift register SR2 successively gives voltage pulses to gate driving wires N1 to N3 to successively switch corresponding reading switches U1 to U3 on, whereby the signals in the first row, which have been transferred to the load capacitors C1 to C3, are converted into serial signals. After impedance conversion by an operational amplifier, the signals of the three pixels are outputted to the outside of the photoelectric conversion apparatus in a period of time T3 (reading operation).
After that, a reset voltage pulse is applied to CRES for time T2 to switch reset switches RES1 to RES3 on and reset the load capacitors C1 to C3, thereby getting ready for the reading operation of the next row (reset operation).
After that, data of all the pixels is outputted by successively driving the gate driving wires G2, G3.
FIG. 3 is a schematic, sectional, structural diagram to show an example of an X-ray detecting apparatus for medical use constructed using the two-dimensional photoelectric conversion apparatus illustrated in FIG. 1. X-rays emitted from X-ray source 1501 are radiated to human body 1502 (affected part of a patient), and transmitted X-rays carrying information corresponding to internal information of lung part, bone part, or lesion travel toward a grid plate 1503. The grid plate 1503 is placed for the purpose of preventing X-rays scattered inside the human body from irradiating a fluorescent member 1504 and the photoelectric conversion apparatus 1506 and is made of a material 1507 absorbing X-rays like lead and a material 1508 transmitting X-rays like aluminum. The X-rays passing through the grid irradiate a wavelength conversion element, which is the X-ray-to-visible light converting fluorescent member 1504 in this example, to be converted to the visible light there in the sensitive wavelength region of the photoelectric conversion elements 1509. In this way the fluorescence from the X-ray-to-visible light converting fluorescent member is photoelectrically converted by the photoelectric conversion apparatus 1506. Numeral 1509 designates the photoelectric conversion elements, 1510 the switching elements, and 1511 a protective film for protecting the photoelectric conversion elements and the switching elements. Numeral 1512 denotes an insulating substrate on which the photoelectric conversion elements and the switching elements are placed.
FIG. 4A is a schematic, top plan view to show an example of the photoelectric conversion circuit unit wherein the photoelectric conversion elements and switching elements are made of amorphous silicon semiconductor thin films, and FIG. 4B is a schematic, sectional, structural diagram to show a cross section along 4Bxe2x80x944B in FIG. 4A. The photoelectric conversion elements 301 and the switching elements 302 (amorphous silicon TFTs, which will be referred to simply as TFTs) are formed on a common substrate 303, the lower electrodes of the photoelectric conversion elements are made of a first metal thin film layer 304 in common with the lower electrodes (gate electrodes) of the TFTs, and the upper electrodes of the photoelectric conversion elements are made of a second metal thin film layer 305 in common with the upper electrodes (the source electrodes and drain electrodes) of the TFTs. The first and second metal thin film layers are also common to the gate driving wires 306 and to the matrix signal wires 307, respectively, in the photoelectric conversion circuit unit. FIG. 4A shows the configuration having the number of pixels being totally four pixels in the matrix of 2xc3x972. In FIG. 4A the hatched portions represent photoreceptive area surfaces of the photoelectric conversion elements. Numeral 309 represents power-source lines for supplying the bias to the photoelectric conversion elements. Numeral 310 indicates contact holes for connection between the photoelectric conversion elements and the TFTs.
Now described is a forming method of the photoelectric conversion circuit unit in the present invention.
First, chromium (Cr) is evaporated as the first metal thin film layer 304 in the thickness of about 500 xc3x85 on the insulating substrate 303 by sputtering or resistance heating, patterned by photolithography, and etched to remove unnecessary areas. This first metal thin layer 304 becomes the lower electrodes of the photoelectric conversion elements 301 and the gate electrodes of the switching elements 302. Next, a-SiNx (311), a-Si:H (312), and n+ layer (313) are successively deposited in the thickness of 3000, 5000, or 1000 xc3x85, respectively, in the same vacuum by CVD. These layers form the insulating layer/photoelectric conversion semiconductor layer/hole injection inhibiting layer of the photoelectric conversion elements 301 and the gate insulating film/semiconductor layer/ohmic contact layer of the switching elements 302 (TFTs). They are also utilized as an insulating layer at cross portions (314 in FIG. 4A) between the first metal thin film layer 304 and the second metal thin film layer 305. The thicknesses of the respective layers do not always have to be limited to the above thicknesses, and are designed so as to be optimal, depending upon the voltage in use as the photoelectric conversion apparatus, the charges, quantities of incident light on the photoreceptive surfaces of the photoelectric conversion elements, and so on. Among others, the a-SiNx layer is desirably not less than 500 xc3x85, in which the layer can prevent electrons and holes at least from passing through and can function well as a gate insulating film of the TFTs. After the deposition of the layers, the areas to become the contact holes (310 in FIG. 4A) are dry-etched by RIE or CDE or the like and thereafter aluminum (Al) is deposited as the second metal thin film layer 305 in the thickness of about 10,000 xc3x85 by sputtering or resistance heating. The layer is further patterned by photolithography and etched to remove unnecessary areas. The second metal thin film layer becomes the upper electrodes of the photoelectric conversion elements 301, the source and drain electrodes of the switching TFTs 302, other wires, and so on. The upper and lower metal thin film layers are connected to each other at the contact hole portions at the same time as the film formation of the second metal thin film layer 305. For forming the channel portions of the TFTs, part of areas between the source electrode and the drain electrode are etched by RIE and thereafter unnecessary a-SiNx layer, a-Si:H layer, and n+ layer are etched away by RIE to separate the elements from each other. This completes the photoelectric conversion elements 301, the switching TFTs 302, the other wires (306, 307, 309), and the contact hole portions 310. Although the sectional view of FIG. 4B shows only two pixels, it is a matter of course that many pixels are formed on the insulating substrate 303 at one time. Finally, the elements and wires are covered by passivation film (protective film) 315 of SiNx in order to enhance moisture resistance. As described above, the photoelectric conversion elements, switching TFTs, and wires are made of the common first metal thin film layer, a-SiNx, a-Si:H, n+ layer, and second metal thin film layer deposited each at one time, and by only etching of the respective layers.
By employing the process using the amorphous silicon semiconductors as principal materials as described above, the photoelectric conversion elements, switching elements, gate driving wires, and matrix signal wires can be made at one time on the same substrate and the photoelectric conversion circuit unit of large area can be provided.
In the photoelectric conversion apparatus, since the operations of transfer, reading, and reset are normally carried out successively in every row unit as described above, the image signals from the photoelectric conversion apparatus are outputted intermittently as indicated by Vout in FIG. 2. Namely, the time necessary for reading of one row is T1+T2+T3 (FIG. 2) and the time for reading of all the bits is three times that in the case of the two-dimensional photoelectric conversion apparatus of 3xc3x973 illustrated in FIG. 1. It is known that the size of the photoelectric conversion apparatus section 1506 of the medical X-ray image pickup apparatus illustrated in FIG. 3 needs to be about 40 cmxc3x9740 cm in the example of the X-ray image pickup apparatus for photographing the lung part. Supposing an image is formed at the pixel pitch of 100 xcexcm, the total number of pixels will be a huge number, 4000xc3x974000=16,000,000 pixels. If the reading operation is carried out simply in the structure illustrated in FIG. 1, the necessary time will be 4000xc3x97(T1+T2+T3). Since the time necessary for T3 is great in practice, it is common practice to provide a plurality of (N) reading circuit units and make the N reading circuit units perform the reading scan in parallel to read all the pixels in the time of 4000xc3x97(T1+T2+T3/N).
FIG. 5 is a schematic diagram of a photoelectric conversion apparatus wherein there are ten reading circuit units provided and the ten units carries out the reading scan in parallel. In this case, the reading circuit units output signals from their associated areas in time series and at the same time. Namely, ten output lines are drawn out of the respective reading circuit units.
It is, however, not easy to produce the many pixels numbering 16,000,000 without a defect of even one pixel, and defective pixels are usually compensated for by interpolation using data of normal adjacent pixels. It is not easy to make the 4000 gate wires and the 4000 matrix signal wires without a discontinuity of even one wire, either. It is thus common practice to interpolate data for outputs of pixels corresponding to a broken wire, using data of normal adjacent pixels.
The load capacitors are illustrated as capacitor elements C1 to C3 in FIG. 1, but they are actually interelectrode capacitances (Cgs) established between the gate electrodes of the switching elements and the electrodes on the matrix signal wire side. Namely, they are capacitances between the upper and lower electrodes on the signal line matrix wire side of TFTs and capacitances established in the cross portions 314 in FIG. 4A. For example, when the signal charge of S1-1 in the first row is transferred, the capacitance of the load capacitor C1 is the sum of the parasitic capacitances Cgs between the upper and lower electrodes on the signal line matrix wire side of the switching elements T1-1, T2-1, and T3-1 dependent upon the signal wire M1 and the capacitances of the respective cross portions placed near the switching elements. Likewise, for example, when the signal charge of S2-2 in the second row is transferred, the capacitance of C2 is the sum of the capacitances Cgs of the switching elements T1-2, T2-2, and T3-2 dependent on the signal wire M2 and the capacitances of the respective cross portions placed near the switching elements. In other words, for transferring a signal charge of any photoelectric conversion element, the load capacitance (C1 to C3) is the sum of three Cgs of the switching elements and three capacitances of the respective cross sections. In similar fashion, in the case of the configuration of the two-dimensional photoelectric conversion apparatus of 4000xc3x974000 pixels, the load capacitance of each signal line in the matrix is the capacitance of (Cgs+capacitance at each cross)xc3x974000. Let Cf represent the load capacitance (the sum of Cgs and capacitances at crosses), Ck represent the capacitance of one photoelectric conversion element, and Qt represent a stored charge. Then, the output potential Vcf after the transfer operation by TFT is given as follows; Vcf=Qt/(Ck+Cf).
FIG. 6 is a top plan view of a photoelectric conversion circuit unit to show an example wherein a matrix signal wire 307 of the photoelectric conversion apparatus illustrated in FIG. 4A has a discontinuity due to anomaly (mixture of dust, foreign matter, or the like) in the film forming step or in the photolithography step. FIG. 7 is a diagram to show a schematic cross section of the circuit unit. In this case, it is impossible for TFTs to carry out the successful transfer operation to transfer the signal charge stored in the photoelectric conversion elements. When there is the discontinuity part as illustrated in FIG. 6, the signal charges of the photoelectric conversion elements up to the discontinuity part can be transferred by the TFTs, but the capacitance of the load capacitor on the matrix signal wire cannot be the normal capacitance because of the discontinuity; that is, Cf becomes small. Therefore, the output Vcf becomes large. Particularly, if the discontinuity part is close to the reading circuit unit, Cf will be very small and the output will be abnormally large. It is a matter of course that the output cannot be transferred from the photoelectric conversion elements located on the far side of the discontinuity part from the reading circuit unit. FIGS. 8(B), (C), and (D) are diagrams to show schematic output examples wherein a discontinuity is present at point B, at point C, or at point D in FIG. 5, and FIG. 8(A) is an output example wherein there is no discontinuity.
FIG. 9 is an example wherein a matrix signal wire 307 of the photoelectric conversion apparatus illustrated in FIG. 6 has a discontinuity due to anomaly (mixture of dust, foreign matter, etc.) in the film forming step or in the photolithography step, which is different from the example of FIG. 7. The difference from FIG. 7 is that the second metal thin film layer 305 forming the matrix signal wire has a discontinuity but the n+ layer below the second metal thin film layer 305 is continuous. In this case, whether the TFT can perform the successful transfer operation to transfer the signal charge stored in the photoelectric conversion element, depends upon the sheet resistance of the n+ layer and the length of the discontinuity of the second metal thin film layer. Specifically, when the length of the discontinuity is long enough, the behavior is similar to that in the example illustrated in FIG. 7. When the length of the discontinuity is very short, the behavior is close to that in the state without discontinuity. In the case of an intermediate discontinuity state between them, the transferred output becomes unstable from the photoelectric conversion elements on the far side of the discontinuity part from the reading circuit unit. The reset operation also becomes unstable from the reading circuit after the transfer operation.
FIG. 10 is the experiment result to show the output of the matrix signal wire in the discontinuity state of FIG. 9. The axis of abscissa is intended to indicate the length of the discontinuity, i.e., the resistance of the n layer, and in the experiment the values were measured by intentionally inserting the resistance between the matrix signal wire without discontinuity and the reading circuit unit. In the measurement the load capacitance was set to about 50 pF. As apparent from this figure, the output at small inserted resistances is equal to that in the state without discontinuity (normal output), while the output at large inserted resistances is close to that in the complete discontinuity state, i.e., the state illustrated in FIG. 7. The stored charge is not transferred in the latter case. In the intermediate range of inserted resistance, the output indicates abnormally high values. This means that there is the possibility that in the discontinuity state with existence of the n+ layer as illustrated in FIG. 9 because of the anomaly (mixture of dust or foreign matter) in the film forming step or in the photolithography step, the output of the signal line could indicate abnormally high values, depending upon the degree of the discontinuity.
When there is a discontinuity in a matrix signal wire, the output of the signal wire is not used as data in the final formation step of an image and the missing data is prepared by the interpolation technology on the software basis or on the hardware basis, normally. For example, the interpolation is often carried out using outputs of adjacent matrix signal wires.
This is also the case in the example of the discontinuity shown in FIG. 7.
There is, however, the following problem. When the reading is carried out in the parallel arrangement of plural reading circuit units as illustrated in FIG. 5, the signal lines from the reading circuit units are normally read in time series and at the same time. If there is the discontinuity illustrated in FIG. 7 or FIG. 9, it will pose the problem of occurrence of so-called cross-talk to affect the adjacent reading circuit units. There are also cases wherein the cross-talk takes place even in the next reading circuit units to the adjacent units. FIG. 11A is an image example in the case of such cross-talk and FIG. 11B shows an output example along the cross section A-B of FIG. 11A. Namely, an output anomaly (c) due to the discontinuity of one line in the photoelectric conversion apparatus induces the cross-talk in several lines (a, b, d, e), which can pose the problem that there are possibilities of inducing degradation of image quality and, in turn, decreasing the yield because of failure in the compensation by interpolation.
The present invention has been accomplished in view of the above problems and an object of the present invention is to solve the problem of degradation of image quality due to the cross-talk in other signal lines, originating in a defective wire.
Another object of the present invention is to solve the problem that presence of wire trouble such as the defective wire or the like disables the whole apparatus and, as a result, make it possible to increase the yield or the like of the photoelectric conversion apparatus and to achieve reduction of cost.
A further object of the present invention is to provide an inexpensive photoelectric conversion apparatus superior in terms of the image and the yield by reducing the cross-talk in the other signal wires by interrupting electrical conduction of a signal wire corresponding to a problematic matrix signal wire in a non photoelectric conversion circuit region in the photoelectric conversion circuit unit or in a non reading circuit region in the reading circuit unit, in order to solve the problem that in the process of forming the photoelectric conversion circuit units on one substrate, the unexpected mixture of dust, foreign matter, or the like caused an unintended defect of discontinuity or the like in the matrix signal wire whereby the photoelectric conversion signal output indicated an inappropriate output value and whereby the output induced the cross-talk in the other signal lines, so as to degrade the image quality and, in turn, decrease the yield.
According to the present invention, when part of plural photoelectric conversion signal outputs from the photoelectric conversion region is inappropriate, the matrix signal wire corresponding to that signal is cut in the non photoelectric conversion region, whereby the cross-talk due to the abnormal output increase in the signal wire can be prevented in the other signal lines, so as to enhance the image quality and increase the yield.
The present invention provides a photoelectric conversion apparatus comprising:
a photoelectric conversion circuit unit in which a plurality of photoelectric conversion elements are arrayed in a matrix; and
a plurality of matrix signal wires for transferring parallel signals outputted from the photoelectric conversion circuit unit to a reading circuit unit;
wherein there is an intentionally cut portion in the matrix signal wire outputting a defective signal, out of said matrix signal wires arranged in a non photoelectric conversion region of said photoelectric conversion circuit unit.
The present invention also provides a photoelectric conversion apparatus comprising:
a photoelectric conversion circuit unit for outputting parallel signals, in which a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate driving wires are placed on one substrate; a driving circuit unit for applying a driving signal to said gate driving wires; and a reading circuit unit for converting the parallel signals transferred through said matrix signal wires to serial signals and outputting the serial signals;
said photoelectric conversion apparatus having a photoelectric conversion region in which said photoelectric conversion elements are placed, and a non photoelectric conversion region in which said matrix signal wires and said gate driving wires except for the part of said photoelectric conversion elements are placed, on said substrate,
wherein there is an intentionally cut portion in the wire part in said non photoelectric conversion region, of said matrix signal wire corresponding to an inappropriate signal out of a plurality of photoelectrically converted signal outputs from said photoelectric conversion region.
The present invention also provides a production method of a photoelectric conversion apparatus, said photoelectric conversion apparatus comprising a photoelectric conversion circuit unit for outputting parallel signals, in which a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate driving wires are placed on one substrate, a driving circuit unit for applying a driving signal to said gate driving wires, and a reading circuit unit for converting the parallel signals transferred through said matrix signal wires to serial signals and outputting the serial signals,
wherein on said substrate there are a photoelectric conversion region in which said photoelectric conversion elements are placed and a non photoelectric conversion region in which said matrix signal wires and said gate driving wires except for the part of said photoelectric conversion elements are placed,
said production method of the photoelectric conversion apparatus comprising such a step that when part of a plurality of photoelectric conversion signal outputs from said photoelectric conversion region is inappropriate, the matrix signal wire corresponding to said signal is cut in the non photoelectric conversion region.
The present invention also provides an information processing apparatus comprising a photoelectric conversion apparatus,
said photoelectric conversion apparatus comprising:
a photoelectric conversion circuit unit in which a plurality of photoelectric conversion elements are arrayed in a matrix; and
a plurality of matrix signal wires for transferring parallel signals outputted from the photoelectric conversion circuit unit to a reading circuit unit;
said information processing apparatus further comprising a wavelength conversion element disposed on the light incidence side of said photoelectric conversion apparatus,
wherein there is an intentionally cut portion in the matrix signal wire outputting a defective signal, out of said matrix signal wires arranged in a non photoelectric conversion region of said photoelectric conversion circuit unit.
The present invention also provides an information processing apparatus comprising a photoelectric conversion apparatus,
said photoelectric conversion apparatus comprising a photoelectric conversion circuit unit for outputting parallel signals, in which a plurality of photoelectric conversion elements, switching elements, matrix signal wires, and gate driving wires are placed on one substrate; a driving circuit unit for applying a driving signal to said gate driving wires; and a reading circuit unit for converting the parallel signals transferred through said matrix signal wires to serial signals and outputting the serial signals;
said photoelectric conversion apparatus having a photoelectric conversion region in which said photoelectric conversion elements are placed, and a non photoelectric conversion region in which said matrix signal wires and said gate driving wires except for the part of said photoelectric conversion elements are placed, on said substrate,
said information processing apparatus further comprising a wavelength conversion element disposed on the light incidence side of said photoelectric conversion apparatus,
wherein there is an intentionally cut portion in the wire part in said non photoelectric conversion region, of said matrix signal wire corresponding to an inappropriate signal, out of a plurality of photoelectrically converted signal outputs from said photoelectric conversion region.
The present invention also provides a photoelectric conversion apparatus comprising a photoelectric conversion circuit in which a plurality of photoelectric conversion elements are arrayed in a matrix, a plurality of matrix signal lines for transferring output signals from the photoelectric conversion circuit, and a reading circuit to which said output signals are transferred,
wherein electrical conduction is interrupted outside the photoelectric conversion circuit between a matrix signal wire having wire trouble and the reading circuit.
The present invention also provides an information processing apparatus comprising a photoelectric conversion apparatus, said photoelectric conversion apparatus comprising a photoelectric conversion circuit in which a plurality of photoelectric conversion elements are arrayed in a matrix, a plurality of matrix signal lines for transferring output signals from the photoelectric conversion circuit, and a reading circuit to which said output signals are transferred,
said information processing apparatus further comprising a wavelength conversion element disposed on the light incidence side of the photoelectric conversion apparatus,
wherein electrical conduction is interrupted outside the photoelectric conversion circuit between a matrix signal wire having wire trouble and the reading circuit.
The present invention also provides a production method of a photoelectric conversion apparatus, said photoelectric conversion apparatus comprising a photoelectric conversion circuit in which a plurality of photoelectric conversion elements are arrayed in a matrix, a plurality of matrix signal lines for transferring output signals from the photoelectric conversion circuit, and a reading circuit to which said output signals are transferred,
said production method comprising such a step that electrical conduction is interrupted outside the photoelectric conversion circuit between a matrix signal wire having a wire trouble and the reading circuit.